The CSS functionality in Opera 9 on Windows XP SP2 allows remote attackers to cause a denial of service (crash) by setting the background property of a DHTML element to a long http or https URL, which triggers memory corruption.
https://exchange.xforce.ibmcloud.com/vulnerabilities/27977
https://euvd.enisa.europa.eu/vulnerability/EUVD-2006-3938
http://www.vupen.com/english/advisories/2006/2987
http://browserfun.blogspot.com/2006/07/mobb-26-opera-css-background.html